Individualized and calibrated air tube for spirometer

ABSTRACT

Disposable air tubes having tracking information disposed thereon or disclosed. Spirometers for reading the tracking information on the disposable air tubes are also disclosed. The tracking information automatically ensures that air tubes are not re-used among different patients. The tracking information thus reduces or eliminates cross-contamination between patients and increases the accuracy of spirometry readings by reducing condensation buildup within the disposable air tubes.

This is a division of application Ser. No. 08/932,739 filed Sep. 17,1997, now U.S. Pat. No. 5,997,483 which is a continuation-in-part ofapplication Ser. No. 08/670,192 filed Jun. 21, 1996 now U.S. Pat. No.5,715,831 and entitled CALIBRATED AIR TUBE FOR SPIROMETER, which iscommonly assigned and the contents of which are expressly incorporatedherein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to air tubes for use with spirometers, andto spirometers using such air tubes. More particularly, the presentinvention relates to air tubes which are disposable and at leastpartially biodegradable, and to calibration and tracking techniques forensuring a high level of accuracy when the disposable air tubes are usedwith the spirometers.

2. Description of Related Art

Spirometers are devices used to measure the volume and flow rate of gasexhaled and inhaled by a user or patient, for example, a human being.Two general types of spirometers measure volume and flow, respectively.For the flow type, the actual port of the spirometer used to measureflow is the pneumotach of which Fleisch is one type. These measurementsare important for physiological studies and for diagnostic analysis ofthe pulmonary performance of the spirometer user. For example, theeffects of various medicines used to treat patients with pulmonary orasthmatic problems can be analyzed by monitoring the volume and flowrate of gas exhaled before and after the administration of medication.Several devices are available on the market which are known aspneumotachs, such as the Fleisch Pneumotach. These devices depend on alaminar air flow past a resistance element. Other spirometers employmore sophisticated electronics so that laminar flow is not needed.

Measuring the pressure difference or differential pressure of exhaledgas across an element which creates or causes the pressure difference isthe basis for differential pressure spirometers. In such differentialpressure spirometers, it is important that the air tube (pneumotach) beprecisely configured and positioned, for example, relative to thepressure sensing and electronics systems of the spirometers so thatmeasurements can be reliably and reproducibly made. Such preciselyconfigured pneumotachs, rather than being disposable, are made out ofmetals or durable plastics to be long lasting and effective after manyuses without structural degradation. See, for example, Waterson et alU.S. Pat. No. 5,137,026, the disclosure of which is hereby incorporatedin its entirety by reference herein.

Since most spirometers involve passing exhaled gas directly from therespiratory system of a user into the instrument for measuring, oneimportant complication of using such devices is contamination from onepatient to another patient if the same spirometer is employed by both.Various approaches to overcoming this contamination problem have beensuggested. A particularly popular approach is to use a disposablemouthpiece and/or bacterial filter over the inlet to the spirometer. Thepatient using the spirometer comes in contact only with the mouthpieceand/or bacterial filter and is able, at least in theory, to avoidcontaminating the remainder of the device. Drawbacks to this approachinclude the relative expense of such mouthpieces/filters, and therelative inefficiency of such systems.

Another approach to overcoming this contamination problem is tosterilize in-between patients the portion or portions of the spirometerwhich come in contact with the user and/or exhaled air. Drawbacks tothis approach include having to spend additional capital onsterilization equipment and supplies, having to monitor the operationand efficacy of the sterilization equipment, and having to purchaserelatively durable and expensive spirometers to withstand thesterilization procedures.

A third alternative that has been suggested is the use of disposablespirometer components. See, for example, Norlien et al U.S. Pat. No.5,038,773; Acorn et al U.S. Pat. No. 5,305,762; Karpowicz U.S. Pat. Des.No. 272,184; Boehringer et al U.S. Pat. No. 4,807,641; and Bieganski etal U.S. Pat. No. 4,905,709. Such previous disposable spirometercomponents have generally been made out of durable plastics or medicalgrade metals so that, even though they are disposable, the cost ofproducing such components is relatively high. In addition, suchdisposable components are relatively difficult to dispose of, forexample, because they are made of durable and long lasting materials.

An element of human error can exist to introduce contamination into aspirometer system, even with the use of disposable spirometercomponents. For example, a user who does not dispose of an air tubeafter use and, instead, leaves the air tube in the spirometer forsubsequent use by another patient, can cause the subsequent patient tobe contaminated. The subsequent use of the air tube can also introduceexcessive condensation into the air tube, which can result in inaccuratespirometry readings.

The economical manufacture of a relatively inexpensive spirometercomponent from a low cost and/or biodegradable material has heretoforebeen prohibitive because of, for example, quality control concerns.General industry specifications require high quality spirometercomponents but the quality of these components can decrease as thecomponents are made biodegradable, for example, placement of thesecomponents within the spirometer can also present problems. Theplacement of the resistive element within each air tube can affect theperformance of the overall spirometer, for example. The resistiveelement should be placed in a normal or perpendicular configurationrelative to the interior wall of the air tube and, further, should beplaced at exact, predetermined distances from the two opposing ends ofthe air tube. Prior art resistive elements often do not exhibit linearresistance-versus-flow-rate responses. More particularly, resistiveelements configured to exhibit good resistance at high flow rates oftendo not perform adequately at low flow rates and, on the other hand,resistive elements configured to perform well at low flow rates often donot provide ideal resistance at high flow rates. Thus, any possibilityof manufacturing a relatively inexpensive spirometer, as an alternativeto the existing durable plastic or metal non-biodegradable components ofthe prior art, would appear to be vitiated due to manufacturing andperformance concerns. These manufacturing concerns include theinconsistencies between various disposable, biodegradable spirometercomponents that may be produced on an assembly line and, further,include subsequent performance variances between the spirometercomponents resulting from these inconsistencies.

Inconsistencies in these components may be augmented when they areassembled together or placed into the spirometer. For example, athroughport of an air tube may not be perfectly formed, and thesubsequent placement of this throughport onto the spirometer mayintroduce abnormally low pressure readings due to air leakage around thepressure port. Even placement of the resistive element within the airtube, as another example, may not be exact between various assembliesand, accordingly, a problem of accuracy may even be prevalent amongexisting durable plastic or metal non-biodegradable components as well.Accordingly, it would be advantageous to provide a means of ensuringhigh performance quality and consistency between various spirometercomponents from an assembly line, regardless of whether the spirometercomponents are metal, plastic, or biodegradable.

SUMMARY OF THE INVENTION

New calibrated air tubes for use in spirometers and spirometersincluding such calibrated air tubes have been discovered. The presentcalibrated air tubes are disposable so that after use by a patient, theyare removed from the spirometer and disposed. Tracking means areincorporated into the spirometer and/or the air tube to ensure that theair tubes are disposed of after use. The tracking means can reduce oreliminate cross-contamination between patients and can increase accuracyby reducing condensation accumulation in the air tube. Each air tube isprovided with individualized calibration information. The spirometer canmemorize the calibration information on a given air tube upon use ofthat air tube, for example, and compare that memorized calibrationinformation with calibration information on subsequent air tubes toensure that a previously-used air tube is not reinserted into thespirometer. Alternatively, special tracking information can be placed onan air tube in addition to or as an alternative to the calibrationinformation.

The air tubes are preferably almost completely biodegradable, can bemanufactured relatively economically, and are capable of yielding highand consistent performance characteristics. As used herein, the term"biodegradable" means that the component or material is decomposableinto more environmentally acceptable components, such as carbon dioxide,water, methane and the like, by natural biological processes, such asmicrobial action, for example, if exposed to typical landfillconditions, in no more than five years, is preferably no more than threeyears, and still more preferably no more than one year.

Having the calibrated air tube biodegradable provides substantialadvantages. First, when the air tube and resistive elements are disposedof, the burden on the environment of such disposal is reduced relativeto, for example, a non-biodegradable air tube, such as those made out ofconventional plastics or metals. In addition, because the air tube andresistive elements are biodegradable, they can be made of materialswhich are inexpensive and plentiful (readily available). Thus, thepresent air tubes are relatively inexpensive, easy and straightforwardto produce. Subsequent calibration of the air tubes accounts for anydiscrepancies in size, shape, and performance of the air tubes.

Since the present air tubes can be made economically, replacing a usedair tube with a new air tube is done without substantial economicimpact. In addition, the present air tubes can be replaced in thespirometer very easily. These advantages promote operator compliance inthat the spirometer operator (for example, the care provider or thepatient operating the spirometer) is more likely to change the presentair tubes after each patient or treatment, thus reducing the risks ofcontamination and the spread of diseases, for example, tuberculosis andother respiratory system disorders, AIDS, other systemic conditions andthe like.

Spirometers employing the present calibrated air tubes provide costeffective, reliable and reproducible (from air tube to air tube)measurements of the pulmonary performance of the user, with reduced riskof contamination. In short, the present disposable, biodegradablecalibrated air tubes are inexpensive and easy to produce to acceptablyprecise specifications (for reproducible performance), are effective andreliable in use, and are conveniently and effectively disposed of in anenvironmentally acceptable or safe manner to reduce the risks ofcontamination caused by spirometer use.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a spirometer in accordance with the presentinvention showing a portion of the electronics disposed apart from thehand held unit.

FIG. 1A is a front side view of the spirometer shown in FIG. 1.

FIG. 2 is an exploded view of the air tube of the present invention;

FIG. 3 is a cross-sectional view of the air tube of the presentinvention;

FIG. 4 is a top planar view of the resistive element of the presentinvention;

FIG. 5 is a partially cut away, top front view, in perspective, of theair tube used in the spirometer shown in FIG. 1.

FIG. 6 is a somewhat schematic illustration showing a spirometer inaccordance with the present invention.

FIG. 6A is a cross-sectional view taken generally along line 6A--6A ofFIG. 6.

FIG. 7 is a cross-sectional view taken generally along line 7--7 of FIG.1.

FIG. 8 is a side view of an alternative embodiment of a spirometer inaccordance with the present invention.

FIG. 9 is a back side view of the spirometer shown in FIG. 8.

FIG. 10 is a perspective view illustrating the bar code reading assemblyof the spirometer of the presently preferred embodiment;

FIG. 11 is a circuit diagram illustrating a specific implementation ofthe bar code reading assembly of FIG. 10;

FIG. 12 is a schematic representation of a linear array of photodiodesfor receiving light from a bar code label according to the presentlypreferred embodiment; and

FIG. 13 is a perspective view of a self focusing lens array used forfocusing light onto the linear array of photodiodes, according to thepresently preferred embodiment.

FIGS. 14 and 15 illustrate perspective views of a spirometer designaccording to the presently preferred embodiment.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring to FIGS. 1 and 1A, a spirometer in accordance with the presentinvention, shown generally at 10, includes a disposable, biodegradableair tube 12, a housing 14 and control electronics 16. Spirometer 10 iswhat is commonly known as a differential pressure spirometer and, ingeneral, operates in a manner similar to the spirometer disclosed in theabove-noted Waterson et al U.S. Pat. No. 5,137,026.

The air tube 12 is described with reference to FIGS. 2 and 3. The airtube 12 includes a first tubular segment 18, a second tubular segment20, and a collar tube 21. A resistive element 22 fits between the firsttubular segment 18 and the second tubular segment 20. The air tube 12and resistive element 22 are preferably approximately ninety-ninepercent biodegradable. The tubular segments 18, 20, and 21 are made ofbiodegradable cardboard or heavy paper, for example, in a manner similarto how cardboard tubes are conventionally made, such as for use withbathroom tissue and the like products. These segments 18, 20, and 21 arepreferably coated with a glossy layer. The resistive element 22preferably comprises biodegradable material having good memorycharacteristics. As presently embodied, the resistive element 22comprises a Nomex material. The resistive element 22 material may,alternatively, comprise any nylon or other material which is somewhatresistant to moisture. As presently embodied, the resistive element 22is approximately 0.003 inches thick, but other thicknesses may be usedaccording to design parameters.

The resistive element 22 is first secured to either the first tubularsegment 18 or the second tubular segment 20, and then the other tubularsegment 18 or 20 is then secured to the resistive element 22. Abiodegradable adhesive is preferably used. As presently embodied, anouter diameter of the first tubular segment 18 is equal to an outerdiameter of the second tubular segment 20, and the outer diameter of theresistive element 22 is equal to the outer diameter of the first tubularsegment 18.

An inner diameter of the collar tube 21 is approximately equal to theouter diameter of the first tubular segment 18. The collar tube 21 isadapted to fit over both the first tubular segment 18 and the secondtubular segment 20. Although adhesives are preferably used for securingthe resistive element 22 between the first tubular segment 18 and thesecond tubular segment 20, the close, frictional fit of the collar tube21 over the first tubular segment 18 and the second tubular segment 20may be sufficient, alone, to secure the resistive element 22 between thefirst tubular segment 18 and the second tubular segment 20.

The distal end 23 of the collar tube 21 is flush with the distal end 25of the first tubular segment 18, when the collar tube 21 is properlysecured over both the first tubular segment 18 and the second tubularsegment 20. Additionally, a notch 27, which preferably comprises apunched out semicircle in the distal end 23 of the collar tube 21, ispreferably lined up with a port 24 of the second tubular segment. Theport 24 of the second tubular segment 20 preferably comprises a punchedout circle in the second tubular segment 20. The notch 27 and/or theport 24 may be formed in the collar tube 21 and/or the second tubularsegment 20 either before or after assembly of the three pieces 18, 20,and 21. After assembly of the three elements 18, 20, and 21. The port 24opens directly into a hollow space (FIG. 3) of the air tube 12.

FIG. 3 illustrates the air tube 12 in an assembled state. Although athree piece configuration of the air tube 12 is presently preferred,these three pieces 18, 20, and 21 may be replaced by a single tube, forexample, and/or the resistive element 22 may be secured to an annularring (not shown), which is inserted within the single tube.

FIG. 4 illustrates a top planar view of the resistive element 22,according to the presently preferred embodiment. The resistive element22 comprises a center aperture 32 and a plurality of slots 34 extendingradially from the center aperture 32. Each pair of adjacent slots 34forms a hinged window 36, which as presently embodied comprises anarrowhead shape. Each arrowhead-shaped hinged window 36 comprises apoint located near the center aperture 32 and a neck 38 located distallyof the center aperture 32. As presently embodied, the resistive element22 comprises eight hinged windows 36, but greater or fewer numbers ofhinged windows 36 may be used according to design parameters. The widthof each neck 38 controls the flexibility of the corresponding hingedwindow 36. A larger neck renders the corresponding hinged window 36 lessflexible, and a smaller neck 38 renders the corresponding hinged window36 more flexible.

A human patient blowing into an end of the air tube 12 generates an airflow through the resistive element 22 which, typically, may comprises anair flow rate of between zero and 16 liters per second. The resistanceprovided by the resistive element 22 should, ideally, be approximatelylinear among these various air flow rates. Prior art resistive elements,comprising a disk with a single aperture therein, for example, do nothave linear pressure versus flow rate relationships. A prior art diskshaped resistive element having a good resistance of less than 1.5centimeters of water per liter per second at approximately 12 liters persecond, for example, will not have a good resistance at lower flowrates. More particularly, such a conventional disk shaped resistiveelement would have a very low resistance at low flow rates, which isunacceptable.

The resistive element 22 of the present invention utilizes unique hingedwindows 36 having necks 38, which can be engineered to tailor theresistance of the resistive element 22 at various flow rates. Theresistive element 22 of the present invention is adapted to provide anideal resistance of less than 1.5 centimeters of water per liter persecond at a flow rate of approximately 12 liters per second but, incontrast to a conventional disk shaped resistive element, the resistiveelement 22 of the present invention also provides good resistance at lowflow rates. Generally speaking, the resistive element 22 provides a verygood, approximately linear flow-rate-versus-resistance response for flowrates between zero and 16 liters per second. At high flow rates, thehinged windows 36 open widely to provide a good resistance that is nottoo high. At low flow rates, the hinged windows 36 open very little, tothereby provide a good resistance that is not too low.

According to the presently preferred embodiment, an angle between two ofthe slots 34 is approximately 45 degrees, and each of the slots 34 has awidth of approximately 0.02 inches. A preferred width of each of theperpendicular hinged portions 37, which is used to control the width ofa neck 38, is approximately 0.04 inches. The diameter of the resistiveelement 22 is preferably 1.09 inches plus or minus 0.0005 inches, and awidth between a line 39 bisecting one of the hinged windows 36, andanother line 41 passing through a slot 34 is approximately 0.0625 inchesplus or minus 0.005 inches.

One important element of the resistive element 22 of the presentinvention is the resistance supplied at low flow rates, since,typically, unhealthy patients are unable to generate high flow rates.The same resistive element also functions well at high flow rates. Theresistive element 22 provides good resistance at various flow rates,regardless of whether the patient is exhaling or inhaling.

Referring to FIG. 5, air tube 12 includes an open inlet 46 and an openoutlet 48. The area surrounding the open inlet 46 is sized and adaptedto be fitted into a human being's mouth. This mouthpiece area isemployed by the patient using spirometer 10 (FIG. 1) by placing the area46 into the mouth and exhaling into hollow space 30 of the air tube 12.

Turning back to FIG. 1, when it is desired to use air tube 12, it isunpackaged and is coupled to housing 14. In particular, the air tube 12is coupled to the housing tube 51. The housing tube 51 includes a tab52, which is adapted to fit within the notch 27 (FIG. 2) of the air tube12. Before the air tube 12 is placed into the housing tube 51, the notch27 is aligned with the port 24 (FIG. 2) and, as presently embodied, ismanually aligned by the user just before insertion into the housing tube51. When the notch 27 is aligned with the port 24, the port 24 willalign with the pressure sensing leg 76, as shown in FIG. 6. Moreparticularly, a fitting of the pressure sensing leg 76, which preferablycomprises a suction cup shape 77 which fits around the port 24 for anairtight fit. The suction cup shaped fitting 77 preferably comprisessilicone rubber or vinyl, and is adapted to provide a good fit aroundthe port 24, to thereby attenuate any leakage of air at this interface.Consequently, breath from the patient is not introduced into thepressure sensing leg 76 and contamination of the pressure sensing leg 76is avoided.

After the notch 27 of the air tube 12 is placed within the housing tube51 and, more particularly, placed over the alignment tab 52, the distalend 23 of the collar tube 21 should be flush with the distal end of thehousing tube 51. At this point, spirometer 10 is ready for use. Notethat air tube 12 is longer than housing tube 51 and, when properlycoupled to the housing tube, extends beyond one end of the housing tube.The relatively long air tube 12 reduces the risk of air exhaled from thespirometer user coming into effective contact with and contaminating thehousing.

FIG. 6 illustrates the general operation of a spirometer, showngenerally at 10. The following is a general description of the operationof the spirometer 10 after the air tube 12 is properly located andpositioned relative to the pressure sensing leg 76. The calibrationmethod and apparatus of the present invention will subsequently bediscussed in further detail after the general operational overview nowprovided. This general description is applicable using any spirometer,such as spirometer 10, in accordance with the present invention. Throughport 24 (FIG. 2) communicates with pressure sensing leg 76. As a furtherprotection against contamination, pressure sensing leg 76 may beequipped with a filter, although this is not required. The pressuresensing leg 76 communicates with a differential or "gauge" type pressuretransducer 80, which may be, for example, a transducer sold by Motorolaunder the trademark MPX 2020D. The pressure transducer 80 generates anelectrical signal on a pair of output wires 82 and 84, which signal isproportional to the differential pressure between pressure sensing leg76 and a sensed atmosphere pressure. This signal is amplified by adifferential amplifier stage 86 and fed into an analog-to-digitalconvertor 88 which converts the amplifier output into digital signals.

The output from convertor 88 is fed to a microprocessor 90, which ispart of control electronics 16. The microprocessor 90 uses calibrationdata supplied by coded information on the air tube 12 in combinationwith an algorithm stored in a ROM 92 to perform several calculations onthe signal from convertor 88, and to display the calibrated finalresults, e.g., volume and flow rate, on display 94, for example, aconventional monitor or liquid crystal display module. Microprocessor 90is powered by a power source 91, for example, either a battery or aconnector capable of being coupled or connected to a source ofconventional electric line voltage. Switch 96 can be activated toinitiate the operation of the spirometer through microprocessor 90. Theresults during each measurement may be stored in a RAM 98 for futurereference. An input/output port 100 may also be provided to allow forchanging the programming of the microprocessor 90. Furthermore, themicroprocessor 90 may be programmed so that on command it may downloadthe results accumulated in RAM 98 through input/output port 100 to aprinter or a computer. Waterson et al U.S. Pat. No. 5,137,026 providesdetails regarding the operation of a conventional spirometer. When apatient has concluded one treatment or diagnostic exercise using thespirometer 10, the biodegradable air tube 12 is removed from the housingtube and is disposed of in an environmentally safe manner.

As shown in FIGS. 1 and 1A, the housing 14 is structured to be grippedin one hand of the user. For example, the shaft 102 of housing 14 isconfigured for easy hand gripping. In addition, finger indents 104 areprovided to make hand holding this device even easier. The fingerindents 104 can be placed in different places in alternativeembodiments, or can be omitted altogether in other alternativeembodiments.

The embodiment shown in FIGS. 1 and 1A includes control electronics 16located within the hand held housing 14. Communication with externalcomputers or printers can occur through cable 106 which can be connectedto the convertor using a jack 105, such as a conventional RJ-11 quickconnect jack, on housing 14. As presently preferred, communication canalso occur through an additional infrared data association (IRDA) link,which is conventional, and operable between the housing 14 and theexternal computer or printer. The electronics in the housing 14 arepreferably powered by a battery pack, such as a conventionalrechargeable nickel-cadmium battery. If such a battery pack is used, thehousing 14 includes a port through which the battery pack can becharged.

In the embodiment shown in FIGS. 1 and 1A, microprocessor 90 can be adedicated microprocessor including a transparent-overlay keypadstructured and adapted specifically to control the operation of aspirometer. Alternatively, the microprocessor 90 may be a component of ageneral purpose, personal computer including a full-sized keyboard,video monitor, hard disk drive and printer. The dedicated microprocessoris particularly advantageous because of its relative simplicity, reducedcost and ease of use. In addition, the shaft 102 of housing 14 includesa tapered portion 107, as shown in FIG. 1A, which facilitates placingand maintaining the housing on a flat surface, for example, betweenuses.

The embodiment shown in FIGS. 1 and 1A is useful as a completely newspirometer, or the air tube 12 and housing 14 can be used to retrofit anexisting spirometer. For example, an existing spirometer includes a handheld unit including a permanent breathing tube, pressure sensing leg, apressure transducer, an amplifier and an analog-to-digital convertor,and is connected to a dedicated control system, which functions in amanner substantially similar to control electronics 16. Simply byreplacing the existing hand held unit with housing 14 and the componentscoupled to or disposed in the housing, a retrofitted spirometer isproduced which has many of the advantages of the present invention. FIG.7 shows a cross-sectional view of the spirometer 10 of FIG. 1, takenalong line 7--7 of FIG. 1.

Another embodiment is illustrated in FIGS. 8 and 9. This spirometer,shown generally at 210, is, except as expressly stated herein,structured in a manner similar to spirometer 10. Components ofspirometer 210 which correspond to components of spirometer 10 havecorresponding reference numerals increased by 200.

The primary differences between spirometer 210 and spirometer 10 have todo with the configuration of air tube 212 and the configuration of thehousing tube 251. Air tube 212 is structured substantially similar toair tube 12 except that in the region near open outlet 248, twopositioning ports 107 and 108 are provided. Housing tube 251 isstructured to act as a cradle for air tube 212 rather than surroundingthe air tube 212, as does housing tube 51. In addition, housing tube 251includes two upwardly extending projections 109 and 110 which arepositioned to be received by positioning ports 107 and 108,respectively, when air tube 212 is coupled to housing tube 251. Withprojections 109 and 110 mated to or received by positioning ports 107and 108, the port 224 (not shown) is properly aligned with the pressuresensing leg 276 (not shown).

As shown in FIGS. 8 and 9, a transparent-overlay control keypad 112 ofmicroprocessor 90 is located on the shaft 302 of housing 214. Inaddition, this embodiment preferably comprises greater ROM, and thedisplay 94 is located on the housing 214 beneath the transparent-overlaykeypad 112. In spirometer 210, the power source 91 is a battery pack,such as a conventional rechargeable nickel-cadmium battery, and islocated within housing 214. Port 114 on housing 214 is adapted toprovide communication between battery pack 91 and a conventional batterycharger to recharge the battery pack when needed. I/O port 100 is alsocarried by housing 214 and provides convenient communication betweenmicroprocessor 90 and a computer or printer, when it is desired todownload information from electronic circuitry 111 to such other device.As with the embodiment of FIG. 1, an IRDA optical port is also disposedon the shaft 302. Spirometer 210 is a self-contained unit that can beoperated by a single patient.

In order to operate spirometer 210, air tube 212 is coupled to housingtube 251 so that projections 109 and 110 mate with positioning ports 107and 108, respectively. The patient then activates a switch on thetransparent-overlay keypad 112 and uses spirometer 210 for any treatmentand/or diagnostic procedure desired. When it is desired to remove airtube 212 from housing tube 251, the biodegradable air tube 212 is simplypicked up from the housing tube 212 and can be discarded in anenvironmentally acceptable manner. Referring again to FIG. 6, acharacter recognition unit 304 is disposed within the housing 14 of thespirometer 10. The character recognition unit 304 preferably comprises adevice for recognizing bar-code-like stripes. The character recognitionunit 304 is disposed within the housing 14 to align with a charactersequence 306, preferably bar-code-like stripes, on the air tube 12, whenthe air tube 12 is placed within the housing 14. According to thepresent invention, calibration information and/or tracking informationrelating to the air tube 12 is coded within the character sequence 306.This coded information is read by the character recognition unit 304 andis conveyed to the converter 88 via line 308 and then to themicroprocessor 90. The converter 88 preferably comprises eight inputs.Of these eight, two receive pressure transducer 80 signals, one receivesflow tube pressure, and one is for rhinomanometry (nasal air pressure).The input for rhinomanometry can be used to accept a pulse oximetryinput in an alternative embodiment. As presently embodied, the characterrecognition unit 304 is disposed within the housing 14 of the spirometer10 to automatically read the character sequence 306, but, alternatively,this reading of information from the character sequence 306 may beperformed manually. Human-readable characters may be disposed next tothe character sequence 306, for example. Additionally, the reading ofinformation from the character sequence 306 may be performed before,during, or after each reading by the spirometer 10, according to designpreference.

After an operation of the spirometer 10 has been performed, the air tube12 should be disposed in accordance with the present invention. Disposalof each air tube after each use reduces or avoids cross-contamination ofpatients. Disposal of each air tube after use can also reducecondensation build up in the air tube, to thereby increase accuracy. Inthe presently preferred embodiment, the spirometer 10 comparesinformation in the character sequence 306 of each new air tube 12 to besure that a new character sequence 306 is present. Information from thecharacter sequence 306 is thus preferably read by the characterrecognition unit 304 before each operation of the spirometer 10. Theinformation read by the character recognition unit 304 is stored in theRAM 98 for future reference. If a new character sequence 306 is notdetected, the spirometer 10 assumes that the air tube 12 has not beenreplaced after the previous reading.

The character recognition unit 304 reads information in the charactersequence 306 before each new operation of the spirometer 10, to ensurethat the previously-used air tube has been removed. If the informationin the character sequence 306 corresponds to the information stored inthe RAM 98, corresponding to the previously-read character sequence 306,then a determination is made that the previously-used air tube is stillpresent. Upon such a determination that the previously-used air tube hasnot been removed, the spirometer 10 will cease to operate in whole or inpart, in accordance with the present invention. For example, thespirometer 10 may refuse to provide a reading until a new, un-used airtube is installed. Alternatively, a warning will be activated such as avisual or audible alarm. In another embodiment, the spirometer willcease to operate in whole or in part, and an alarm will be activated.

The spirometer 10 can comprise a comparator for comparing each entirecharacter sequence 306 of each air tube, or can be configured to compareonly a portion of each character sequence 306 of each air tube toprevent re-use. A unique tracking character or tracking charactersequence is preferably provided within each character sequence 306, inaddition to calibration information. The spirometer 10 may be programmedto keep a log of past air tubes which have been read. For example, thespirometer 10 may be configured to keep a log of the past 100 air tubeswhich have been read by the spirometer 10. Before each new operation ofthe spirometer, information in the new character sequence is comparedwith information in the character sequences of the past 100 air tubes toensure that an old air tube is not being re-used.

The character recognition unit 304 is preferably an optical characterrecognition unit, adapted for reading a bar code character sequence 306but, alternatively, other information conveying techniques may beimplemented. For example, magnetic character recognition, opticalalphanumeric character recognition, optical symbol recognition, etc. maybe used, so long as calibration information relating to the air tube 12is conveyed to the microprocessor 90. Preferably, the characterrecognition unit 304 comprises a linear array for recognizing bar-typecodes.

FIG. 6A illustrates a cross sectional view taken along line 6A--6A ofFIG. 6. As presently embodied, a light source 310 projects light in thedirection of the arrow A1 onto a character sequence 306 disposed on asurface of the air tube 12. As presently embodied, the charactersequence 306 comprises a bar code label or, alternatively, a bar codeprinted directly onto the air tube 12. The light from the light source310 reflects from the character sequence 306 in a direction of the arrowA2 and enters a self focusing lens array 313. Light from the selffocusing lens array 313 is subsequently focused onto a linear array ofphotodiodes 315. The linear array of photodiodes generates an electricaloutput, which is subsequently interpreted by the converter 88 and thenby the microprocessor 90 (FIG. 6) to discern tracking information and/orcalibration information contained within the character sequence 306.According to the presently preferred embodiment, a wedge shaped blackplastic holder 318 is disposed between the light source 310, and theself focusing lens array 313, and the linear array of photodiodes 315.The wedge shaped black plastic holder 318 is adapted for securing thesethree elements 310, 313, and 315 thereto for proper alignment within thehousing 14 of the spirometer 10.

A perspective view of the character recognition unit 304 of thepresently preferred embodiment is illustrated in FIG. 10. Light from thelight source 310 is focused onto the character sequence 306 disposed onthe air tube 12. Reflective light is received by the self focusing lensarray 313, which, as presently embodied, is disposed at an angle 321 ofapproximately 45 degrees from the light source 310. Both the lightsource 310 and the self focusing lens array 313 have lengths which aresubstantially parallel to a center line scan 323 passing through thecharacter sequence 306.

The linear array of photodiodes 315 is disposed substantially parallelto the self focusing lens array 313, and is adapted for receivingfocused light from the self focusing lens array 313. An extraneous lightstop 325 is disposed over a portion of the self focusing lens array 313,and another extraneous light stop 327 is disposed over the linear arrayof photodiodes 315.

FIG. 13 illustrates the clip-on light stop 325 adapted for accommodatingthe self-focusing lens array 313, according to the presently preferredembodiment. The light stop 325 preferably comprises black plastic, andmay be frictionally fit around the self-focusing lens array 313 and/orsecured thereto using an adhesive. Alternatively, less expensive lightstop techniques may be implemented, according to design preference. Asmentioned previously with reference to FIG. 6A, both the light source310 and the self focusing lens array 313 and, more preferably, also thelinear array of photodiodes 315, are disposed on a wedge shaped blackplastic holder 318. The wedge shaped black plastic holder 318 providesthe correct angle between the light source 310, and the self focusinglens array 313 and the linear array of photodiodes 315. The wedge shapedblack plastic holder 318 further facilitates proper spacing of the lightsource 310, the self focusing lens array 313, and the linear array ofphotodiodes 315 from each other and from the air tube 12. The wedgeshaped black plastic holder preferably comprises a black color forsuppressing light reflections. The total conjugate focal length 333 ofthe self focusing lens array 313 is preferably approximately 9.4millimeters, measured from an internal sensitive surface of the lineararray of photodiodes 315 to the target surface of the character sequence306. As presently embodied, the self focusing lens array 313 comprises aSelfoc® lens array, manufactured by Nippon Sheet Glass Co., Ltd. Thisself focusing lens array 313 is positioned midway between the lineararray of photodiodes 315 and the character sequence 306 so that both thelinear array of photodiodes 315 and the character sequence 306 are atfocal points of the self focusing lens array 313. As presently embodied,the self focusing lens array 313 is positioned 2.5 millimeters from thecharacter sequence 306 and 2.5 millimeters from the linear array ofphotodiodes 315.

An approximately 1 millimeter wide portion of the character sequence 306image along the character sequence center line 323 is transferred by theself focusing lens array 313 to the linear array of photodiodes 315 whenthe character sequence 306 is illuminated by the light source 310. Aspresently embodied, the self focusing lens array 313 is approximately 18to 20 millimeters in length, and comprises a single row of lenses 336.The self focusing lens array 313 is preferably slightly longer than thelinear array of photodiodes 315, which is approximately 16 millimetersin length, to insure that the entire linear array of photodiodes 315receives an image, allowing for a plus or minus 1 millimetermisalignment and/or end lens damage on the self focusing lens array 313.Although the above-described orientations, distances, and tolerances arepreferred, different orientations, distances, and tolerances may beimplemented in alternative embodiments to generate similar results. Thetwo focal points of an exemplary individual lens 336 of the selffocusing lens array 313, which are not to scale, are shown at 339 and340.

The linear array of photodiodes 315 preferably comprises an intelligentoptical sensor manufactured by Texas Instruments, model number TSL215,and comprising an array of 128 charge-mode pixels in a 128×1 lineararray. The linear array of photodiodes 315 is preferred over a chargecoupled device (CCD) because of ease of use, among other reasons. Thelinear array of photodiodes 315 comprises integrated clock generators,analog output buffers, and sample and hold circuitry that wouldotherwise be required by a CCD circuit. The focal point 340, forexample, is focused approximately 1 millimeter beneath the top surfaceof the linear array of photodiodes 315.

As presently embodied, in addition to the extraneous light stop 327, aclear plastic packaging 344 is disposed over the sensitive surface 346,as illustrated in FIG. 12. The center scan line 323 is projected ontothe sensitive surface 346, as shown by the line 348. As presentlyembodied, the focal point 340 (FIG. 10) is approximately 1 millimeterbeneath the top surface of the clear plastic packaging 344, and isprojected onto the sensitive surface 346 of the array.

Light is projected onto the sensitive surface 346 of the linear array ofphotodiodes 315 when the light source 310 is activated by themicroprocessor 90 (FIG. 6). As illustrated in FIG. 11, themicroprocessor 90 activates the light source 310 using the"illumination-on" signal line 350, which is connected to a parallel portpin 352 of the microprocessor 90. As presently embodied, the lightsource 310 comprises a four element light emitting diode array ofapproximately 45 millicandelas (lumens/ster), having a wavelength ofapproximately 635 nanometers and being approximately a lambertiansource. The light source 310 is biased with a 20 milliamps of current onthe middle two lamps and 25 milliamps of current on the end lamps, toprovide an even illumination along the character sequence 306, accordingto the present invention. The light source 310 provides approximately 23microwatts per square centimeter of illumination, and is positionedapproximately 7 millimeters from the target bar code, as illustrated byreference numeral 354. The light stop 325 between the light source 310and the self focusing lens array 313 suppresses stray light. The presentinvention incorporates a 635 nanometer wave length to roughly match thesensor peak responsivity of the linear array of photodiodes 315 which isapproximately 750 nanometers. The sensitivity obtained in the lineararray of photodiodes 315 is approximately 80% of the 100% maximum lineararray sensitivity at 750 nanometers wave length. The light source 310has a length of approximately 16 millimeters. As presently embodied, thelight source 310 is only activated by the microprocessor 90 during barcode reads, since, obviously, activation of the light source 310dissipates power. Both the light source 310 and the linear array ofphotodiodes 315 preferably comprise integrated circuits that are mountedon a flexible PC board, and form a dihedral angle 321 with respect toeach other of 45%.

Referring to FIG. 11, the image integration time of the linear array ofphotodiodes 315 begins with a short pulse on line 360 by themicroprocessor 90 into the serial input pin 362 of the linear array ofphotodiodes 315. After approximately 1 to 10 milliseconds, a secondserial input pulse is input into the linear array of photodiodes 315 online 360. After this second serial input pulse, the image is read on thevideo output pin 364 by clocking the clock pin 366 at between 10kilohertz and 100 kilohertz, using 129 or more clock pulses. Theresulting signal is placed on the serial video output line 368. Duringthe above-mentioned clocking operation, the serial video output, whichcomprises an analog voltage, is read by the analog to digital (A/D)converter 370, which preferably comprises 12 bit accuracy and a 0 to 5volt input range. The analog to digital converter 370 outputs digitaldata on data bus 373, which reflects the amplitude of each video pulseand, consequently, the darkness of each sensor pixel of the linear arrayof photodiodes 315. This digital data on data bus 373 is subsequentlyread by the microprocessor 90. The analog to digital converter 370 iscontrolled by the microprocessor 90, and has a conversion time ofapproximately 10 microseconds. Accordingly, the linear array ofphotodiodes 315 can be clocked at up to 10 microseconds (100 kilohertz).

The linear array of photodiodes 315 is powered by a 3 terminal voltageregulator 375 to maintain power supply noise and video array noise at aminimum. Although the Texas Instruments TSL215 is presently preferred, anewer Texas Instruments product, the TSL1402 may be used instead. Thislater model comprises twice an many pixels in the same length of 16millimeters. The model has twice the resolution and will allow for moredigits and more reliability. This later model is pin compatible, so thatthe number of clock cycles can simply be changed from 129 to 257, and isless susceptible to optical saturation. The TSL1402 further does notrequire the 40 millisecond initial pixel charge period, and wouldprovide double the speed and accuracy.

The character sequence 306 preferably comprises a bar code having eitheran Interleaved 2 of 5 ITF sequence, providing approximately 3 decimaldigits of calibration data plus a check sum digit or, alternatively, maycomprise a straight binary code. The straight binary bar code ispresently preferred, and is configured to provide approximately five andone half digits plus a binary check sum of about six bits. The binarycode will be NRZ (non-return-to-zero) with constant width bars andspaces, plus a starting mark. This configuration ensures that the totalwidth of the code is constant and allows 1 millimeter on each side forcode positioning error. The minimum white and black bar widths in thebar code are selected to be at least 2 to 3 pixels wide on the lineararray of photodiodes 315. Since the linear array of photodiodes has aspacing of 0.125 millimeters between photodiodes, the minimum bar widthis approximately twice that width. This configuration ensures that atleast one pixel position in the video output 368 of the linear array ofphotodiodes 315 will go fully low or high, since one pixel in the array315 is fully black or white, and not positioned half way between a blackbar and a white area. The full high or low voltage, in relation to othervoltages in the video output 368 of the linear array of photodiodes 315,is decoded by software to positively indicate a bar position.

Since the light source 310 is preferably of constant intensity,variances in light source intensity between units and over time arecompensated for by the present invention. For this reason, and tocompensate for sensor efficiency, the light integration of the lineararray of photodiodes 315 is adjusted. The level of the image video readfrom the linear array of photodiodes 315 can be increased by increasingthe time between the serial input pulses on line 360, i.e., the time oflight integration interval. After each bar code read, if the bar codeamplitude data is too low, the integration time is adjusted up until theamplitude is sufficient to detect white to black differences. Theoverall amplitude of the whole serial video data stream from each readoperation forms a nonlinear curve, due to changes in light intensityalong the light source. In software, according to the present invention,a running differential average or other indicator indicates theapproximate white to black threshold along the entire video data length.This average will be used to detect white from black data by softwarecomparison. High frequency noise is filtered out by software, and theresulting data stream comprises an image of the bar code. As presentlyembodied, this resulting data stream is decoded by the NRZ binary methodor the interleaved 2 of 5 method, depending on the code used. This NRZformat changes the bar code color if the data bits do not change anddoes not change the bar code color when the bits do change. Theresulting steam, after being decoded by either the NRZ binary method orthe integrated 2 of 5 method, comprises the original binary or decimalnumber that was originally encoded onto the air tube 12. This number isthen used to calibrate this spirometric flow sensor.

The linear array of photodiodes 315 must initially be preconditioned bya 40 millisecond operation period, before each bar code read, to therebyallow for each of the 128 pixels to change from white to black or viceversa, correctly. During this preconditioning period, the light sourceremains on, and the data from the bar code is ignored. Subsequently,several bar code scans are performed until the correct data is obtained,judging by the check sum embedded in the bar code. According, the totalread operation is approximately 40 milliseconds plus 5 milliseconds perbar code scan, or about 100 milliseconds. Each bar scan requires 128times 10 microseconds minimum time, or 128 times 100 microsecondsmaximum time. The time is determined by the required integration time,as mentioned above.

The light source 310 is turned on continually during all bar code scans,up to 100 milliseconds, and is not turned off between individual 5millisecond scans, since the pixels have to be illuminated throughoutthe integration time. An embedded microprocessor 16 bit timer isprogrammed to develop 10 to 100 milliseconds repeated time periods, witheach period generating an interrupt. A timer interrupt starts a routinethat outputs the integration start pulse if needed, and then outputs 129clock pulses, timed by the timer. At each clock pulse, the analog todigital converter 370 is read by the microprocessor 90 via data bus 373and stored for later analysis. After completion of the 129 clock pulses,the timer is stopped and the data is analyzed by the microprocessor 90to find the moving white-black threshold level, for each pixel, usingcontinuous filtering and averaging. The data is then filtered insoftware and compared to the moving threshold level, before beingconverted into bar codes. In the presently preferred embodiment,approximately 8 bar code scans are taken and stored at a time, requiring8 times 12.5 milliseconds, or 100 milliseconds maximum time, so that the40 milliseconds initial pixel charge time does not have to be repeated.

Regarding the self-focusing lens array 313, this assembly may have to beadjusted to focus exactly on the character sequence 306 within plus orminus 0.3 millimeters, unless this is guaranteed by the manufacturingprocess. The focal distance may have to be adjusted in a low lightenvironment, while a diagnostic program runs on the microprocessor 90and continually scans the character sequence 306, outputing thepercentage of read errors from reading the character sequence 306. Thisfocal distance is preferably adjusted until the errors are minimized.Worst case or random bar code examples would preferably be used for thisprocedure.

According to the method of calibrating a subject air tube 12 and placingthe calibration information onto the air tube 12 in the form of acharacter sequence 306, a large initial sample lot of air tubes 12 froma manufacturing line are tested. As presently embodied, the testingprocedure comprises subjecting each flow tube 12 to an air stream of 7.5liters per second in the expiratory direction. A sensor leg, similar tothat shown in FIG. 6 at 76, is placed over the through port 24 (FIG. 2)of the air tube 12, and this sensing leg is connected to a high-accuracypressure sensor. A mechanical resonance filter may be required in thetube. The measured pressure, in response to the air stream of 7.5 litersper second in the expiratory direction, is noted for each tube and,subsequently, a similar measured pressure for the same air flow rate inthe inspiratory direction is obtained for each air tube 12.

The present invention recognizes that, although manufacturingdifferences exist between each air tube 12, the pressure output versusairflow input curve for each air tube 12 is remarkably similar. Moreparticularly, this pressure output versus air flow input curve for eachflow tube 12 can be mathematically modeled by a third order polynomialwith fixed coefficients. The polynomial for each air tube 12 varies byonly a single gain factor. Thus, according to the presently preferredembodiment, the response of any subject air tube may be calibrated toreplicate an ideal or model response by merely multiplying the responseof the subject air tube by a constant.

Since the pressure output versus air flow input curve for each air tube12 varies only by a constant, the measured pressure of a subject airtube 12 can be compensated to achieve an ideal pressure output, for anygiven air flow rate between 0 and 16 liters per second. Although thepresent invention is described in a particular embodiment wherecalibration of each subject air tube can be performed by merelygenerating a single calibration constant for each air flow direction(inspiratory and expiratory), the present invention is not limited tothis exemplary embodiment.

According to the presently preferred embodiment, after pressuremeasurements for air flow rates in the inspiratory direction and theexpiratory direction are obtained for a subject air tube 12, these twopressure measurements are compared with two corresponding model pressuremeasurements. The model pressure measurements are obtained by averagingpressure measurements of a large initial sample lot of flow tubes 12from the manufacturing line, as presently preferred. A gain factor isdetermined, based upon the tube pressure measurement of the subject airtube 12 and the tube model pressure measurements. For example, if themodel pressure measurement for the inspiratory direction is slightlyhigher than the subject tube pressure measurement for the inspiratorydirection, a correction factor is generated to increase the pressuremeasurement of the subject tube 12 to the model pressure measurement.This correction factor comprises a constant in the presently preferredembodiment. A look-up table having a number of subject-air-tube 12measurements and corresponding correction factors may be used, as justone example. As presently embodied, such a look-up table may comprise alarge number of subject tube pressure measurements according to desiredaccuracy, and corresponding correction factors. The correction factors,as presently embodied, calibrate each subject tube to a desired accuracylevel. Still further, according to the presently preferred embodiment, asingle binary number is used to represent both correction factors forany subject air tube 12. Since the subject air tube 12 is tested for ameasured pressure in both the inspiratory direction and the expiratorydirection, two different correction factors will be generated,corresponding to the two measured pressure rates of the subject air tube12. The single binary number is presently preferred to represent thesetwo correction factors in a compressed form, and may also be obtainedfrom a look-up table.

FIGS. 14 and 15 illustrate perspective views of a spirometer designaccording to the presently preferred embodiment. The air tube 212 issubstantially covered by the housing, and the display 94 andtransparent-overlay keypad 112 are larger than in previously describedembodiments.

This invention has been described with respect to various specificexamples and embodiments. Alternative embodiments may comprise differentequipment, orientations, distances, and tolerances, so long as theinformation on the air tubes can be automatically read. It is to beunderstood that the invention is not limited thereto and that it can bevariously practiced with the scope of the following claims.

What is claimed is:
 1. A spirometer adapted for being operativelycoupled to an air tube, the spirometer comprising:a coupling memberconstructed to contact and be operatively coupled to an air tube havingtracking information; a character recognition unit operatively coupledto the spirometer and constructed to automatically read the trackinginformation; circuitry adapted to determine whether the air tube haspreviously been used in the spirometer by comparing the read trackinginformation with at least one reference value, the at least onereference value comprising tracking information which was previouslyread from another air tube by the character recognition unit; and amemory for storing the at least one reference value.
 2. The spirometeras recited in claim 1, the spirometer further comprising means fordisabling the spirometer upon a determination by the circuitry that theair tube has been previously used in the spirometer.
 3. The spirometeras recited in claim 1, the spirometer further comprising means foractivating an alarm of the spirometer upon a determination by thecircuitry that the air tube has been previously used in the spirometer.4. The spirometer as recited in claim 1, wherein:the coupling member isadapted for removably holding an air tube having a pressure response andmachine-readable calibration information relating to the pressureresponse of the air tube; and the character recognition unit is adaptedto automatically read the calibration information.
 5. The spirometer asrecited in claim 4, wherein the spirometer further comprises:a pressuresensing assembly adapted to sense a pressure in the air tube held by thecoupling member and to provide pressure data based at least in part onthe pressure in the air tube.
 6. The spirometer as recited in claim 5,wherein the circuitry is adapted to automatically process thecalibration information read by the character recognition unit, thecircuitry being adapted to use the read calibration information toautomatically correct the pressure response of the air tube held by thecoupling member to a pressure response of a model air tube having aconfiguration and dimensions which are substantially similar to the airtube held by the coupling member.
 7. A spirometer adapted for beingoperatively coupled to an air tube, the spirometer comprising:a couplingmember constructed to contact and be operatively coupled to an air tubehaving tracking information; a character recognition unit operativelycoupled to the spirometer and constructed to automatically read thetracking information; circuitry adapted to determine whether the airtube has previously been used in the spirometer by comparing the readtracking information with at least one reference value, the at least onereference value comprising a plurality of reference values correspondingto tracking information which was previously read from an individual airtube by the character recognition unit; and a memory for storing the atleast one reference value.